1. Field of the Invention
The present invention relates in general to audio data processing and in particular, to digital audio decoding circuitry and methods and systems using the same.
2. Description of the Related Art
The ability to process audio information has become increasingly important in the personal computer (PC) environment. Among other things, audio is important in many multimedia applications, such as gaming and telecommunications. Audio functionality is therefore typically available on most conventional PCs, either in the form of an add-on audio board or as a standard feature provided on the motherboard itself. In fact, PC users increasingly expect not only audio functionality but high quality sound capability. Additionally, digital audio plays a significant role outside the traditional PC realm, such as in compact disk players, VCRs and televisions. As the audio technology progresses, digital applications are increasingly sophisticated as improvements in sound quality and sound effects are sought.
One of the key components in many digital audio information processing systems is the decoder. Generally, the decoder receives data in a compressed form and converts that data into a decompressed digital form. The decompressed digital data is then passed on for further processing, such as filtering, expansion or mixing, conversion into analog form, and eventually conversion into audible tones. In other words the decoder must provide the proper hardware and software interfaces to communicate with the possible compressed (and decompressed) data sources, as well as the destination digital and/or audio devices. In addition, the decoder must have the proper interfaces required for overall control and debugging by a host microprocessor or microcontroller. Since, there are a number of different audio compression/decompression formats and interface definitions, such as Dolby AC-3 and S/PDIF (Sony/Phillips Digital Interface), a state of the art digital audio decoder should at least be capable of supporting multiple compression/decompression formats.
Digital systems normally require a voltage controlled oscillator or similar clock generation circuitry for establishing the operating time base. To maximize system flexibility, it is desirable to have a variable or tunable clock generator capable of providing variable frequency clocks. This is especially true for devices and systems such as audio decoders which must be adaptable to several operating environments. Since tuning of the clock frequency must be done with some degree of accuracy, the need has arisen for techniques precisely calibrating a voltage controlled oscillator circuitry, particular for those incorporated in audio processing devices.